A sub-field scale critical source area index for legacy phosphorus management using high resolution data

I.A. Thomas, P.-E. Mellander, P.N.C. Murphy, O. Fenton, O. Shine, F. Djodjic, P. Dunlop, P. Jordan

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

Diffuse phosphorus (P) mitigation in agricultural catchments should be targeted at critical source areas (CSAs) that consider source and transport factors. However, development of CSA identification needs to consider the mobilisation potential of legacy soil P sources at the field scale, and the control of (micro)topography on runoff generation and hydrological connectivity at the sub-field scale. To address these limitations, a 'next generation' sub-field scale CSA index is presented, which predicts the risk of dissolved P losses in runoff from legacy soil P. The GIS-based CSA Index integrates two factors; mobile soil P concentrations (water extractable P; WEP) and a hydrologically sensitive area (HSA) index. The HSA Index identifies runoff-generating-areas using high resolution LiDAR Digital Elevation Models (DEMs), a soil topographic index (STI) and information on flow sinks and effects on hydrological connectivity. The CSA Index was developed using four intensively monitored agricultural catchments (7.5-11 km2) in Ireland with contrasting agri-environmental conditions. Field scale soil WEP concentrations were estimated using catchment and land use specific relationships with Morgan P concentrations. In-stream total reactive P (TRP) concentrations and discharge were measured sub-hourly at catchment outlet bankside analysers and gauging stations during winter closed periods for fertiliser spreading in 2009-14, and hydrograph/loadograph separation methods were used to estimate TRP loads and proportions from quickflow (surface runoff). A strong relationship between TRP concentrations in quickflow and soil WEP concentrations (r2 = 0.73) was used to predict dissolved P concentrations in runoff at the field scale, which were then multiplied by the HSA Index to generate sub-field scale CSA Index maps. Evaluation of the tool showed a very strong relationship between the total CSA Index value within the HSA and the total TRP load in quickflow (r2 = 0.86). Using a CSA Index threshold value of ≥0.5, the CSA approach identified 1.1-5.6% of catchment areas at highest risk of legacy soil P transfers, compared with 4.0-26.5% of catchment areas based on an existing approach that uses above agronomic optimum soil P status. The tool could be used to aid cost-effective targeting of sub-field scale mitigation measures and best management practices at delivery points of CSA pathways to reduce dissolved P losses from legacy P stores and support sustainable agricultural production.
LanguageEnglish
Pages238 - 252
JournalAgriculture, Ecosystems & Environment
Volume233
Early online date25 Sep 2016
DOIs
Publication statusPublished - 3 Oct 2016

Fingerprint

phosphorus
runoff
soil
agricultural watersheds
agricultural catchment
connectivity
microrelief
index
digital elevation models
best management practices
catchment
sustainable agriculture
Ireland
microtopography
best management practice
hydrograph
land use
agricultural production
targeting
fertilizers

Keywords

  • Critical source area
  • Diffuse pollution
  • Phosphorus
  • LiDAR DEM
  • Agriculture
  • Hydrologically sensitive area

Cite this

Thomas, I. A., Mellander, P-E., Murphy, P. N. C., Fenton, O., Shine, O., Djodjic, F., ... Jordan, P. (2016). A sub-field scale critical source area index for legacy phosphorus management using high resolution data. 233, 238 - 252. https://doi.org/10.1016/j.agee.2016.09.012
Thomas, I.A. ; Mellander, P.-E. ; Murphy, P.N.C. ; Fenton, O. ; Shine, O. ; Djodjic, F. ; Dunlop, P. ; Jordan, P. / A sub-field scale critical source area index for legacy phosphorus management using high resolution data. 2016 ; Vol. 233. pp. 238 - 252.
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A sub-field scale critical source area index for legacy phosphorus management using high resolution data. / Thomas, I.A.; Mellander, P.-E.; Murphy, P.N.C.; Fenton, O.; Shine, O.; Djodjic, F.; Dunlop, P.; Jordan, P.

Vol. 233, 03.10.2016, p. 238 - 252.

Research output: Contribution to journalArticle

TY - JOUR

T1 - A sub-field scale critical source area index for legacy phosphorus management using high resolution data

AU - Thomas, I.A.

AU - Mellander, P.-E.

AU - Murphy, P.N.C.

AU - Fenton, O.

AU - Shine, O.

AU - Djodjic, F.

AU - Dunlop, P.

AU - Jordan, P.

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N2 - Diffuse phosphorus (P) mitigation in agricultural catchments should be targeted at critical source areas (CSAs) that consider source and transport factors. However, development of CSA identification needs to consider the mobilisation potential of legacy soil P sources at the field scale, and the control of (micro)topography on runoff generation and hydrological connectivity at the sub-field scale. To address these limitations, a 'next generation' sub-field scale CSA index is presented, which predicts the risk of dissolved P losses in runoff from legacy soil P. The GIS-based CSA Index integrates two factors; mobile soil P concentrations (water extractable P; WEP) and a hydrologically sensitive area (HSA) index. The HSA Index identifies runoff-generating-areas using high resolution LiDAR Digital Elevation Models (DEMs), a soil topographic index (STI) and information on flow sinks and effects on hydrological connectivity. The CSA Index was developed using four intensively monitored agricultural catchments (7.5-11 km2) in Ireland with contrasting agri-environmental conditions. Field scale soil WEP concentrations were estimated using catchment and land use specific relationships with Morgan P concentrations. In-stream total reactive P (TRP) concentrations and discharge were measured sub-hourly at catchment outlet bankside analysers and gauging stations during winter closed periods for fertiliser spreading in 2009-14, and hydrograph/loadograph separation methods were used to estimate TRP loads and proportions from quickflow (surface runoff). A strong relationship between TRP concentrations in quickflow and soil WEP concentrations (r2 = 0.73) was used to predict dissolved P concentrations in runoff at the field scale, which were then multiplied by the HSA Index to generate sub-field scale CSA Index maps. Evaluation of the tool showed a very strong relationship between the total CSA Index value within the HSA and the total TRP load in quickflow (r2 = 0.86). Using a CSA Index threshold value of ≥0.5, the CSA approach identified 1.1-5.6% of catchment areas at highest risk of legacy soil P transfers, compared with 4.0-26.5% of catchment areas based on an existing approach that uses above agronomic optimum soil P status. The tool could be used to aid cost-effective targeting of sub-field scale mitigation measures and best management practices at delivery points of CSA pathways to reduce dissolved P losses from legacy P stores and support sustainable agricultural production.

AB - Diffuse phosphorus (P) mitigation in agricultural catchments should be targeted at critical source areas (CSAs) that consider source and transport factors. However, development of CSA identification needs to consider the mobilisation potential of legacy soil P sources at the field scale, and the control of (micro)topography on runoff generation and hydrological connectivity at the sub-field scale. To address these limitations, a 'next generation' sub-field scale CSA index is presented, which predicts the risk of dissolved P losses in runoff from legacy soil P. The GIS-based CSA Index integrates two factors; mobile soil P concentrations (water extractable P; WEP) and a hydrologically sensitive area (HSA) index. The HSA Index identifies runoff-generating-areas using high resolution LiDAR Digital Elevation Models (DEMs), a soil topographic index (STI) and information on flow sinks and effects on hydrological connectivity. The CSA Index was developed using four intensively monitored agricultural catchments (7.5-11 km2) in Ireland with contrasting agri-environmental conditions. Field scale soil WEP concentrations were estimated using catchment and land use specific relationships with Morgan P concentrations. In-stream total reactive P (TRP) concentrations and discharge were measured sub-hourly at catchment outlet bankside analysers and gauging stations during winter closed periods for fertiliser spreading in 2009-14, and hydrograph/loadograph separation methods were used to estimate TRP loads and proportions from quickflow (surface runoff). A strong relationship between TRP concentrations in quickflow and soil WEP concentrations (r2 = 0.73) was used to predict dissolved P concentrations in runoff at the field scale, which were then multiplied by the HSA Index to generate sub-field scale CSA Index maps. Evaluation of the tool showed a very strong relationship between the total CSA Index value within the HSA and the total TRP load in quickflow (r2 = 0.86). Using a CSA Index threshold value of ≥0.5, the CSA approach identified 1.1-5.6% of catchment areas at highest risk of legacy soil P transfers, compared with 4.0-26.5% of catchment areas based on an existing approach that uses above agronomic optimum soil P status. The tool could be used to aid cost-effective targeting of sub-field scale mitigation measures and best management practices at delivery points of CSA pathways to reduce dissolved P losses from legacy P stores and support sustainable agricultural production.

KW - Critical source area

KW - Diffuse pollution

KW - Phosphorus

KW - LiDAR DEM

KW - Agriculture

KW - Hydrologically sensitive area

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DO - 10.1016/j.agee.2016.09.012

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Thomas IA, Mellander P-E, Murphy PNC, Fenton O, Shine O, Djodjic F et al. A sub-field scale critical source area index for legacy phosphorus management using high resolution data. 2016 Oct 3;233:238 - 252. https://doi.org/10.1016/j.agee.2016.09.012